The present invention relates to the employment of impedance spectroscopy to determine the chemical condition of lubricating fluids as, for example the condition of lubricants used in an internal combustion engine.
A known technique for monitoring in real time the condition of engine lubricant is described in U.S. Pat. No. 6,278,281 assigned to the assignee of the present invention and which describes using the differential of current measurements or impedance for separate current measurements taken at high and low frequencies indicative respectively of bulk fluid and electrode surface impedance. Such differential impedance spectroscopy has proven to be a useful technique for enabling a transducer to provide a continuous signal indicative of the engine lubricant during operation of the engine.
However, it has been found that there is also the need to readily identify the presence of any engine coolant leaking from the engine coolant system into the engine lubricant.
Although the aforesaid known technique of differential impedance spectroscopy has been found useful for monitoring changes in engine lubricant due to the effect of products of combustion, it has not be found limited to tracking such effects.
The aforesaid technique is described in U.S. Pat. No. 6,278,281 although useful, has not been found satisfactory for detecting the presence of coolant in the engine lubricant and it has been found quite difficult to rationalize the behavior of the fluid over a range of temperatures where the amount of coolant contamination is varying due to progressive leakage into the engine lubricant. Thus, it has been desired to provide a simple, low cost and easy to install way or means of correlating the changes in the engine lubricant due to engine coolant contamination and in order to provide an accurate real time indication of the amount of coolant contamination in the engine lubricant.